In modular automation systems, it is desirable to adapt the input and output components of the system to the conditions prevailing in a given industrial process with regard to the use of actuators and sensors. To do so, the CPU of the system must determine the type of configuration to determine the consistency between a projected structure assumed in the user program and the actual structure, e.g. for diagnostic purposes. International patent application WO 94/15299 describes an arrangement with a CPU that detects whether functional units have been plugged into the module slots of the arrangement. For this purpose, the plug-in units have level switching devices that switch the level of the address line assigned to them in the event the units receive a module slot identification signal from the CPU during the read access time.
To reduce the number of input and output components installed in automation systems despite a high degree of expansion, decentralized peripheral systems are used, e.g., in the form of an "active terminal." A case with peripheral modules is moved to the process actuators and sensors, and only one interface module, which is connected to the decentralized peripheral system by a cable, is necessary in the automation unit. The arrangement proposed in international patent application WO 94/15299 can detect whether the interface connection is plugged into a module slot in the automation unit, but it cannot recognize whether the peripheral modules are present in the decentralized peripheral system.
The object of the present invention is to create an arrangement of the type defined in the preamble, wherein an installed or plug-in functional unit can be identified. In addition, an identifiable functional unit is to be created that can be identified even if it is set up at a separate location from its signal processing connection.
Additional embodiments of the present invention are derived from the subclaims.
The device of the functional unit may be designed to be active or passive. An active device has the means for producing an identification signal from a voltage generated in the device itself. A passive device, however, converts a voltage supplied by the signal processing connection into an identification voltage. The voltage of the interface connection and the identification voltage are preferably transmitted over the available signal line.
The present invention as well as embodiments and advantages are explained in greater detail below with reference to the figures, which illustrate one embodiment of the present invention.